When a person at rest breathes, approximately 500ml of air is exchanged between the lungs and the environment; the full capacity of the lungs is not exchanged with each breath. When the person exercises and increases breathing rate and depth, greater amounts of air are exchanged. Here is more information on the amounts and the medical terms for each: https://en.wikipedia.org/wiki/Lung_volumes.

So in a way the "residual volume" could be described as "stale," although it is not the exact same molecules that stay in the lungs with each breath. Hope that makes sense.